1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Thermodynamics Hw help, piston designing

  1. Nov 17, 2012 #1
    1. The problem statement, all variables and given/known data
    Have a design project in thermodynamics. The problem reads,

    Someone has suggested that the device shown in the figure below be used to improve the maximum force F against the spring, which has a spring constant of k. This is accomplished by changing the temperature of the liquid-vapor mixture in the container. You are to design such a device to close sun-blocking window-shutters that require a maximum force of 0.5 lbf. The piston must move 6 inches to close those shutters completely. You elect to use R-134a as the working fluid and arrange the liquid-vapor mixture container such that he temperature changes from 70 degrees F when shaded from the sun to 100 degrees F when exposed to the full sun. Select the sizes of the various components in this system to do this task. Also select the necessary spring constant and the amount of R-134a to be used.


    2. Relevant equations

    Force=pressure*Area
    Force=k*x

    3. The attempt at a solution
    All of my work and all the info I have been using is in the attachments. I have been working it on a whiteboard at school. I can only load 3 pics. I continued on and found that the natural length of the spring is 9.707 inches with a k value of 0.031833 Lbf/in.

    I am assuming that at 100 degrees F that the system is in equilibrium and the force to keep the windows closed is 0.5 lbf. The picture also shows the piston is closed off, so I am assuming that I don't need to worry about atmospheric pressure. I can't see where I am going wrong, but the piston diameter seems to small. Is this right or am I reading the original problem wrong.
     

    Attached Files:

    • 1.JPG
      1.JPG
      File size:
      34.2 KB
      Views:
      163
    • 2.JPG
      2.JPG
      File size:
      29 KB
      Views:
      178
    • 3.JPG
      3.JPG
      File size:
      24.6 KB
      Views:
      159
  2. jcsd
  3. Nov 19, 2012 #2
    Got it figured out.
     
  4. May 21, 2013 #3
    I have assignment as what you did. So can you please give me your answer? so I can get some ideas. Please Help me.
     
  5. Nov 25, 2013 #4
    Hi Nilkc, i have the same project and i'm having trouble with that, could you give me a hint?? hELP
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Thermodynamics Hw help, piston designing
Loading...